1. Field of the Invention
The present invention relates to an apparatus for controlling the vibration of a steel sheet being driven along the running surface of a processing facility in a steel rolling line or surface treating line in a steel mill.
2. Description of the Related Art
FIG. 27 shows a schematic diagram of a conventional apparatus for controlling the vibration of a steel sheet 101 being processed, by placing opposing electromagnets 102A, 102B on the front and back sides across the steel sheet 101.
In such an apparatus, sensors 107A, 107B are placed inside the electromagnets 102A, 102B, respectively, for detecting the distances from the steel sheet 101 to respective electromagnets 102A, 102B, and the excitation currents passing through the coils in the electromagnets 102A, 102B are controlled according to the distances detected by the sensors 107A, 107B, so that the magnetic attraction forces can be adjusted in such a way to reduce the vibrations.
This vibration control apparatus comprises a plurality of pairs of electromagnets 102xcx9c105 arranged transversely to the running direction of the steel sheet, as seen in a plan view of the steel sheet 101 shown in FIG. 28. Pairs of sensors 107xcx9c110 are placed in paired electromagnets 102xcx9c105 so that the magnitudes of the excitation current can be adjusted according to respective separation distances detected by the paired sensors.
In such a vibration control apparatus, because of bowing in the steel being rolled, the path of the steel sheet can sometimes show a tendency to be closer to one or the other electromagnet depending on the type of steel being processed and the running speed. If the control of electromagnets is started under such a condition, the control apparatus, in its effort to correct bowing of the steel sheet, tries to deliver more current to the electromagnet that is farther away from the sheet. However, a considerable force is required when the steel sheet is thick so that it is necessary to supply a high current to develop the necessary magnitude of force. Under such a circumstance, excitation current may become saturated due to factors such as inadequate capacity of the amplifier for the electromagnet, which may result in virtual loss of vibration control.
Also, when starting or stopping the vibration control action of the apparatus, if the apparatus is simply turned on or off, the excitation current changes suddenly to cause the steel sheet to hunt for a balancing position thus resulting in wild oscillation, and in extreme cases, the surface of the steel may collide with the surface of the magnetic poles to cause scratches on the steel sheet.
Also, when starting the control action, if the steel sheet is vibrating with such a large amplitude that the electromagnets cannot be brought into a proper range for control action, it may be considered that the electromagnets may be brought into proper positions after starting the process line. However, if the gap is large and the steel sheet is outside the range of detection of the sensors and the sensors are not able to detect the sheet position properly, there is a possibility that the steel sheet can be induced into oscillation.
Also, in the control apparatus described above, the relationship between the electromagnet pairs and the running sheet is subject to continual change because of such factors as the variations in the sheet thickness and width of the steel roll to be processed. For this reason, if the gain of the control apparatus is fixed at a constant value, changes in thickness, for example, may make the steel sheet susceptible to vibration to such an extent that the sheet surface may touch the pole surfaces of the electromagnets, in some cases.
Also, widthwise snaking of the steel sheet may occur in such a way that the edge of the steel sheet 101 swings to the position shown by the dotted line in FIG. 28. In such a case, the steel sheet 101 positions itself in an ambiguous-location between the pair of electromagnets 102 so that, in spite of the fact that the sensor pair 107 inside the electromagnet pair 102 cannot detect the distances to the steel sheet, the control action in this case would be based on the detected distance of the sensor pair 107 to the steel sheet, therefore, control action on the electromagnet pair 102 becomes impossible. Under such a circumstance, the steel sheet may undergo vibration or the surface of the sheet 101 may touch the pole surfaces of the electromagnet pair 102 to cause scratches on the sheet 101.
Also, if the steel sheet moves completely out of the detection range of the pair of electromagnet placed near the edge of the steel sheet, power will be wasted by the pair of electromagnets that are out of the range of detecting the steel sheet.
All of the foregoing problems may also be caused by changes in the width of the steel sheet being processed, for example.
Also, this type of control apparatus is normally operated so that the steel sheet would pass through the center line between the pair of opposing electromagnets. But, when the type of steel being processed changes in a given roll, that is, when a welded joint is passing through, the electromagnets are sometimes moved away from their normal detection position to a standby position to avoid collision of the welded section with the electromagnets. If the move is made while the electromagnets are turned on, even though the position of the steel line has not changed, the relative distances between the steel sheet and the electromagnets would increase, so that the control apparatus judges that the steel sheet has moved in a direction away from the sensors, and increases the excitation current to the electromagnets.
In this case, because the electromagnets are moving away from the steel sheet, the current increases as the electromagnets are moved away, and ultimately the control apparatus capability reaches its saturation limit, and the apparatus becomes inoperable. In the worst case scenario, the magnets may be overheated and destroyed.
To avoid such phenomena from happening, power to the conventional apparatus is turned off when the electromagnets are to be moved to the standby position. In the absence of vibration control action, vibration can be introduced in the processing line, and particularly during the initial stage of preparing for the standby operation, in other words, while the distance of separation between the electromagnets and the steel sheet is small, there is a danger that the steel sheet may contact the electromagnets.
It is an object of the present invention to provide an apparatus for controlling vibration of a steel sheet being processed in a steel processing line, so that the processing line can be operated in a stable manner without having operational problems such as sheet vibration or loss of vibration control caused by such factors as snaking of the steel sheet or changes in the conditions of the sheet such as varying sheet thickness and width in the running sheet.
Also, it is another object of the present invention to provide a vibration control apparatus that permits the electromagnets to be retreated to a standby position without causing a line instability or excessive heating and damage to the electromagnets.
The object has been achieved in an apparatus for controlling vibration comprised by: electromagnet means for generating magnetic forces acting at right angles on the steel sheet; sensor means for detecting separation distances between the steel sheet and the electromagnet means; control means for controlling a flow of excitation current through the electromagnet means according to separation distances detected by the sensor means; and actuator means for adjusting the separation distance between the steel sheet and the electromagnet means; wherein the separation distance is adjusted by the actuator means when a specific condition is attained in a positional relationship between the steel sheet and the electromagnet means.
The present apparatus for controlling vibration may also be comprised by: electromagnet means for generating magnetic forces acting at right angles on the steel sheet; sensor means for detecting separation distances between the steel sheet and the electromagnet means; control means for controlling a flow of driving current through the electromagnet means according to separation distances detected by the sensor means; wherein a circuit gain for controlling the driving current is determined in accordance with information on the steel sheet, including thickness data, running speeds, joint locations, sheet widths and line tension data.
The present apparatus for controlling vibration may also be comprised by: electromagnet means for generating magnetic forces acting at right angles on the steel sheet; sensor means for detecting separation distances between the steel sheet and the electromagnet means; control means for controlling a flow of driving current through the electromagnet means according to a specific command value and separation distances detected by the sensor means; and moving means for moving the electromagnet means transversely to move away from the steel sheet so as to retreat to a standby position or to return to a detection position; wherein the moving means moves the electromagnet means to move away from the steel sheet to the standby position, according to sheet information including welded joint data, and to further perform a return operation to return to the detection position, and the control means alters the position command value when moving the moving means according to a distance to be moved, and further provides a return operation command.
The present apparatus for controlling vibration may also be comprised by: electromagnet means comprised by opposing pairs of electromagnets disposed in proximity of front and back surfaces of the steel sheet for generating magnetic forces acting at right angles to sheet surfaces; sensor means disposed so as to form opposing pairs of sensors for detecting respective separation distances between the steel sheet and the opposing pairs of electromagnets; control means for controlling a flow of driving current through the pairs of electromagnets according to differences in separation distances generated by the opposing pairs of sensors and specific position command values derived from the differences in separation distances; and moving means for moving-the electromagnet means transversely to the steel sheet so as to retreat to a standby position or to return to a detection position; wherein the moving means move the pairs of electromagnets to move away from the steel sheet to the standby position, according to sheet information including joint location data.
Any of the apparatuses described above is able to operate a processing line in a stable manner because an electromagnet requiring a higher flow of steady-state current than others in the sensor array is pushed closer to the sheet, in so doing, the supply of current to the electromagnet, which is most remote from the steel sheet, is reduced thereby reducing the load on the electromagnet and restoring the steady-state operation of the processing line.
The apparatus may be operated according to a condition that when the separation distance between an electromagnet and the sheet exceeds a specific value, an actuator device brings the electromagnet closer to a sheet steel to reduce the steady-state current flowing in the electromagnet to reduce its load to provide a stable vibration control.
The apparatus may be operated so that an electromagnet is moved by actuator means in a direction to nullify the low frequency components or direct current components, thereby reducing the load on the electromagnet and providing a stable operation of the processing line.
The apparatus may be operated so that a separation distance between a steel sheet and electromagnets is adjusted by paired electromagnets opposing each other across a steel sheet without altering the relative positions of the paired electromagnets, thereby reducing the load on the electromagnets and operating the line in a stable manner.
The apparatus may be operated so that, when starting or ending to control the excitation current, the apparatus adjusts the controlling gain and steady-state current in electromagnet means according to a ramp function, thereby preventing the generation of a phenomenon of xe2x80x9chuntingxe2x80x9d, i.e., oscillation of the strip of steel being processed.
The apparatus may be operated so that, when starting or ending to control a flow of excitation current to an electromagnet, the deviation in the steady-state location of an electromagnet in the integration means are reset to a zero, thereby reducing rapid changes in the excitation current and preventing xe2x80x9chuntingxe2x80x9d.
The entire operation of the vibration control apparatus is made smoother by using the present apparatus, because it is possible to bring the electromagnet closer to the steel sheet while soft-starting the vibration control system, or retreating the electromagnet away from the steel sheet by soft-stopping the vibration control means.
The present apparatus is controlled so that the controlling gain is determined according to detected distances of individual sensors, so that it is possible to prevent collision between the steel sheet and the pole surface of the electromagnet due to vibration caused by changes in the sheet condition such as sheet thickness and other parameters of the steel sheet being processed.
Also, internal judging means are provided in the apparatus so that when it is decided that a steel sheet is not present within a given range of a sensor, the controlling gain for this sensor is reduced to zero. For example, when the steel sheet is out of the range of detection of the sensor due to snaking or changes in the sheet width, the apparatus turns off the electromagnet corresponding to this sensor, thereby preventing waste of electrical energy.
Also, when snaking in the widthwise direction of the running sheet causes an uncertainty in detecting the edge of the steel sheet between a pair of electromagnets, the apparatus does not cause the paired electromagnets to become inoperative, thereby preventing loss of control of vibration or damage to the surface by collision of the sheet against the electromagnet.
The present apparatus is provided with a gain table based on information on a variety of steel sheets, including thickness data, running speeds, joint locations, sheet widths and line tension data, so that a controlling gain for each type of steel sheet is determined according to the gain table, thereby preventing vibration and resulting collision between the sheet and the pole surface of the electromagnet.
Also, even if the type of steel sheet varies within a given roll, stable operation can be continued by switching the electromagnets to be operated and suitably adjusting the controlling gain.
Also, if a weld joint is detected indicating a change in the type of steel to be processed, the controlling gain can be altered automatically so that manual alteration by a line operator is not required.
Also, in the present apparatus, the electromagnet means are disposed in such a way that electromagnets disposed on a front-side do not oppose electromagnets disposed on a back-side of a steel sheet, thereby preventing erroneous detection caused by mutual interference between the opposing electromagnets.
Also, the present apparatus is able to retreat the electromagnets to a standby position, or return the electromagnets to the detection position while performing vibration control by varying the position command value in accordance with a separation distance detected by a relevant pair of electromagnets, so that a flow of excessively high excitation current or overheating and damage to the electromagnets can be prevented.
Also, by detecting the separation distance using a pair of electromagnets across the steel sheet, obtaining a difference in the separation distance, and controlling the excitation current in accordance with the difference, the opposing pair of electromagnets can be retreated at the same time without altering the position command value, to prevent a flow of excessively high excitation current or overheating and damage to the electromagnets.
Also, the apparatus includes integration means which can be inactivated when the electromagnets are to be retreated so that even when the separation distance exceeds the sensor detection range, a flow of excessively high excitation current or overheating and damage to the electromagnets can be prevented.